I agree, I feel like it wouldn't actually take 5 hours to change a water pump on anything...let alone be worth $500. The way they time auto repairs is ridiculous, something will book in at .8 of an hour, but in real life it takes double that, meanwhile something else will book at 5 hours and actually only take 3.
I agree - no AC stuff and no air pump junk in the way - unless the bolts were all rusted up and I broke some off, with my tools, unlikely it would take me much more than a couple hours to scrape off old gaskets, change pump and thermostat, flush, refill and bleed system.
BUT - If I was broke down in IA in February, with no enclosed building to work in, and no lift, and I need transportation quick, without my tools, I'd be thinking hard about having someone with a nice shop and tools do it too. Won't take long for rent car, and lost wages to eat up $500.
The conditions he stated left him little time to price the job out or negotiate. He has good idea of cost of an aftermarket pump with a lifetime warranty, and since he has changed water pumps, he knows what is involved.
Hopefully this thread is of value to others in the future.